A variety of polymer-based drug delivery systems for achieving sustained or controlled drug release have been described (See Langer, Nature, 392 (supplement), 5-10, 1998 and references therein). The goal of many of those systems was typically one or more of prolonging drug release, improving drug bioavailability, and/or providing non-injectable drug delivery systems that improve patient compliance and comfort. The polymers, either synthetic or natural, provide delivery of the various agents by various mechanisms, depending on the properties of the polymer.
The polymer-based systems have been variously formulated as, for example, a liquid, a suspension, an emulsion, a powder comprising microparticle and/or microspheres, a film, or a tablet. The compositions have been administered via various routes or methods, including injection, topical administration, or administration to a mucosal surface of the eye, vaginal, anus, stomach or intestines, oral and nasal cavities, or the lungs. The polymer-based systems have been used to deliver a variety of physiologically active agents, including therapeutics and prophylactic agents, including small molecule- or protein-based drugs, nucleic acids, polysaccharides, fatty acids and esters, cells and fragments thereof, viruses, and vaccines for prevention of infectious diseases.
In-situ gelation has been used in pharmaceutical drug delivery systems and involves gel formation at the site of application to a tissue or body fluid after the composition or formulation has been applied, so as to form a bioadhesive gel to modulate the release of the drug from the gel. In some applications, In-situ gelation permits the drug to be delivered in a liquid form.
Polymers capable of in-situ gelation have been described, including Poloxamer, Pluronics (Vadnere et al., Int. J. Pharm., 22, 207-218, 1984), various copolymers such as PEO-PLLA and PEG-PLGA-PEG (Jeong et al., Nature 388, 860-862, 1997; Jeong et al., J. Controlled Release 63, 155-163, 2000), cellulose acetophthalate latex (Gurny et al. J. Controlled Release 353-361, 1985), Gelrite (Rozier et al., Int. J. Pham. 57, 163-168, 1989), Carbopol, and Matrigel. The gel formation is induced by temperature change (Poloxamer, Pluronics, PEO-PLLA diblock copolymer, PEG-PLGA-PEG triblock copolymer, and Matrigel), pH change (cellulose acetophalate latex and Carbopol), or reaction with mono- or di-valent cations (Gelrite and/or alginates). However, most of them require a high polymer concentration for in-situ gel formation (>20%) (Poloxamer, PEO-PLLA diblock copoly, PEG-PLGA-PEG triblock copolymer, cellulose and acetophalate latex). The thermally gelling polymers (Poloxamer, Pluronics, PEO-PLLA diblock copolymer, PEG-PLGA-PEG triblock copolymer, and Matrigel) also have the disadvantage of gelling before administration due to temperature change during packaging or storage. Unfortunately some of these polymers are not biodegradable such as Poloxamer or require manipulation of the temperature before administration (PEO-PLLA diblock copolymer) or during formulation (Pluronics and Gelrite). An ophthalmic in-situ gelling drug delivery formulation consisting of a mixture of Carbopol and Pluronic was found to be more effective than formulations consisting of either one. However, Pluronic is used at 14% (Lin and Sung, Journal of Controlled Release 69, 379-388, 2000). Such polymers are therefore not well suited for medical applications in humans and animals. Furthermore, many of these polymers form only a hydrogel which is a viscous but still flowing solution (e.g., Poloxamer and Pluronics).
The in-situ gelation compositions using ionic polysaccharides has been disclosed in U.S. Pat. No. 5,958,443, which discloses compositions comprising a drug, a film forming polymer and a gel forming ionic polysaccharide (such as an alginate). These compositions employed two separately applied components, one being a solution of crosslinking cations, which is applied to the site, and a second liquid component comprising the drug, film forming polymer and an ionic polysaccharide, which is then applied to react with the cross linking ions and form a gel. Various other synthetic and natural polymers have also been used in drug delivery formulations that may or may not have formed crosslinked gels, including starches and modified celluloses, gellan, chitosan, hyaluronic acids, pectins, and the like.
The use of pectins has been mentioned in various drug delivery compositions. Pectins are a biodegradable acidic polysaccharide isolated from plant cell walls. All vegetables and fruits that have been examined appear to contain pectins. Pectins from sugar beets, sunflowers, potatoes, and grapefruits are just a few other well known examples. The chemistry and biology of pectins have been extensively reviewed (Pilnik and Voragen, Advances in plant biochemistry and biotechnology 1, 219-270, 1992; Voragen et al, In Food polysaccharides and their applications. pp 287-339. Marcel Dekker, Inc. New York, 1995; Schols and Voragen, In Progress in Biotechnology 14. Pectins and pectinases, J. Visser and A. G. J. Voragen (eds.). pp. 3-20. Elsevier Science Publishers B.V. Amsterdam, 1996).
Pectins have an α-(1→4)-linked polygalacturonic acid (Gal A) polysaccharide polymer backbone intervened by rhamnose residues. The Gal A residues have carboxylic acid substituent groups attached to the saccharide ring, which may be in the form of the carboxylic acid, a salt thereof, or an ester thereof. The Gal A content of most pectins is about 70-75%, and the rhamnose content is typically <2%. The rhamnose residues are α-(1→2)-linked to Gal A residues in the backbone, and induce a T-shaped kink in the backbone chain, leading to more flexibility in the polysaccharide chains. Neutral sugar side chains are attached to the rhamnose residues in the backbone, at the O-3 or O-4 position, and the rhamnose residues tend to be clustered together on the backbone. These rhamnose contain regions comprising the side chains is referred to as a “hairy region” of the pectin, while the long stretches of repeating and unbranched Gal A residues are termed the “smooth region” of the pectin.
The hydroxyl and/or carboxylic acid substituents on the saccharide rings are also often bonded to non-sugar components such as methyl and acetyl groups. The extent of rhamnose insertions and other modifications to the chain and its monomers vary depending on the plant source of the pectin. Methylation occurs at carboxyl groups of the Gal A residues, so as to form carboxylic acid methyl esters. The degree of methylation or methyl-esterification (“DM”) if a pectin is defined as the percentage of carboxyl groups (Gal A residues) esterified with methanol. Based on the DM, pectins are divided into two classes, low methoxyl (“LM”) pectin with a DM of <50% and a high methoxyl (“HM”) pectin with a DM of >50%. Most natural pectins and most commercial pectins, which are typically derived from citrus and apples, are HM pectins.
LM pectins are typically obtained from HM pectins through an artificial chemical or biochemical de-esterification process. Commercial LM pectins typically have a DM of 20-50%. A completely de-esterified pectin is referred as “pectic acid” or “polygalacturonic acid”. Pectic acid in the acid form is insoluble but is soluble in the salt form. The common salt form of pectic acid is either sodium or potassium.
Pectins are typically most stable at acidic pH levels between approximately 3-4. Below pH 3, removal of methoxyl and acetyl groups and neutral sugar side chains typically occurs. Under neutral and alkaline conditions, the methyl ester groups of the Gal A residues are known to be saponified to the carboxylic acid or carboxylate form, but the polygalacturonan backbone also breaks through β-elimination-cleavage of glycosidic bonds on the non-reducing ends of methylated Gal A residues, with the result that the molecular weight of LM pectins is typically significantly less than the molecular weight its parent HM pectin. Once formed, pectic acids and LM pectins are relatively more resistant to loss of molecular weight at neutral and alkaline conditions since, there are only limited numbers of methyl ester groups, or none at all, so that β-elimination-cleavage of the polymer chains slows down.
Both HM and LM pectins form gels. However, these gels form via totally different mechanisms (Voragen et al, In Food polysaccharides and their applications. pp 287-339. Marcel Dekker, Inc. New York, 1995). HM pectin forms a gel in the presence of high concentrations of certain co-solutes (for example sucrose) at low pH. HM pectins are typically not reactive with calcium or other multivalent ions and therefore do not form a calcium gel as do the LM pectins (infra). However, certain HM pectins can be made calcium-reactive by a block wise de-esterification process, while still having a DM of >50%. See, Christensen et al. U.S. Pat. No. 6,083,540.
LM pectins, which have high percentages of un-esterified carboxylic acid and/or carboxylate groups, are known to form gels in the presence of sufficient concentrations of calcium cations. The calcium ions are believed to coordinate to anionic carboxylate groups of the Gal A polymer subunits, and thus, are known as “calcium-reactive.” The calcium-LM pectin gel network is believed to be built up by formation of what is commonly referred to as “egg-box” junction zones in which Ca++ causes the coordination and cross-linking of complementary carboxylate groups along two complementary stretches of polygalacturonic acid polymer chains. Calcium-LM pectin gel formation is influenced by several factors, including the DM, ionic strength, pH, and molecular weight of the pectin (Garnier et al., Carbohydrate Research 240, 219-232, 1993; 256, 71-81, 1994). Current commercial LM pectins typically have a molecular weight of 7-14×104 Da and a Gal A content of ˜75% (Voragen et al, In Food polysaccharides and their applications. pp 287-339. Marcel Dekker, Inc. New York, 1995). Typical pectins have a rhamnose content of <2%.
Pectins are typically utilized in the food industry and classified by the FDA as “GRAS” (Generally Regarded As Safe). They have also long been used as colloidal and anti-diarrhea agents. Recently, pectins have been utilized in the areas of medical device and drug delivery (Thakur et al., Critical Reviews in Food Science & Nutrition 37, 47-73, 1997). In the case of drug delivery, pectin has found its presence in many experimental formulations for oral drug delivery to the colon because pectin is readily degraded by bacteria present in this region of the intestines. The pectin is either used directly with no gelation involved, or a pectin calcium gel is pre-formed to encapsulate the drug agent before administration. Ashford et al., J. Controlled Release 26, 213-220, 1993; 30, 225-232, 1994; Munjeri et al., J. Controlled Release 46, 273-278, 1997; Wakerly et al., J. Pharmacy & Pharmacology 49, 622-625, 1997; International Journal of Pharmaceutics 153, 219-224, 1997; Miyazaki et al., International Journal of Pharmaceutics 204, 127-132, 2000.
U.S. Pat. No. 6,432,440 recently disclosed the use of LM pectins in liquid pharmaceutical formulations adapted to gel on contact with mucosal surfaces. U.S. Pat. No. 6,342,251 disclosed the use of a wide variety of polymers, including pectins in liquid and solid formulations for nasal administration of drugs suitable for the treatment of erectile disfunction. U.S. Pat. Nos. 5,707,644 and 5,804,212 recently disclosed the use of many polymers, including pectins, in formulating bioadhesive microspheres for the delivery of pharmaceuticals, peptides, and antigenic vaccines to nasal surfaces, but did not suggest the use of LM pectins or calcium induced gellation on contact with the nasal surfaces. The entire descriptions of U.S. Pat. Nos. 6,432,440, 5,707,644 and 5,804,212 are hereby incorporated herein by this reference, in their entireties, for their teachings regarding the formulation of in-situ gelling pharmaceutical compositions, the pectins used to prepare such compositions, and the administration of the compositions to animals and humans.
Biotechnology and associated methods for delivering drugs and related biopharmaceutical agents has been a subject of intense studies over recent years, but only limited progress has been made in the area of delivery of these agents, especially biopharmaceutical agents. Biopharmaceutical agents, such as peptides, proteins, nucleic acids, vaccines, antigens, and bioengineered cells, microorganisms, and viruses tend to be unstable, both in storage and after application. Injection of such agents into the tissues of an animal or human is sometimes successful, but is often economically and aesthetically undesirable, especially if frequent administrations are required. Many biopharmaceutical agents, especially the larger agents have in the past only been poorly absorbed if administered orally or to mucosal membranes. Once successfully administered to the animal, many biopharmaceutical agents are rapidly degraded by the body before they can effectively exert their desired function, and need protection from degradation and/or the benefits of time release formulations. Therefore, many long felt but as yet unfulfilled needs exist in the area of administration of biopharmaceutical agents.
Thus, a great need exists for a simpler, improved, and/or more efficient in-situ gelling compositions for drug and/or biopharmaceutical agent delivery.